Re: [PATCH v2 01/31] Documentation: document EXPORT_OP_NOLOCKS

Jeff Layton
2026-01-20T14:12:32Z

On Tue, 2026-01-20 at 08:20 -0500, Jeff Layton wrote:
> On Mon, 2026-01-19 at 23:44 -0800, Christoph Hellwig wrote:
> > On Mon, Jan 19, 2026 at 11:26:18AM -0500, Jeff Layton wrote:
> > > + EXPORT_OP_NOLOCKS - Disable file locking on this filesystem. Some
> > > + filesystems cannot properly support file locking as implemented by
> > > + nfsd. A case in point is reexport of NFS itself, which can't be done
> > > + safely without coordinating the grace period handling. Other clustered
> > > + and networked filesystems can be problematic here as well.
> >
> > I'm not sure this is very useful. It really needs to document what
> > locking semantics nfs expects, because otherwise no reader will know
> > if they set this or not.
>
> Fair point. I'll see if I can draft something better. Suggestions
> welcome.

How about this?

+ EXPORT_OP_NOLOCKS - Disable file locking on this filesystem. Filesystems
+ that want to support locking over NFS must support POSIX file locking
+ semantics and must handle lock recovery requests from clients after a
+ reboot. Most local disk, RAM, or pseudo-filesystems use the generic POSIX
+ locking support in the kernel and naturally provide this capability. Network
+ or clustered filesystems usually need special handling to do this properly.

--
Jeff Layton <jlayton@kernel.org>